Blood flow is an extremely important parameter in hyperthermia. It is the primary mode of heat dissipation and, as such, often limits tumor temperatures during hyperthermia to less than 43 degrees C. In addition, the vascular system is the primary mode for delivery of chemotherapeutic agents, oxygen and nutrients to the tumor cells. Considerable data have been reported on the response of blood flow to hyperthermia in transplanted rodent tumors; however, little data exist for spontaneous human tumors. The overall objective of this project is to characterize the response of human tumor blood flow to hyperthermia and establish its relationship to interstitial pH. The hypotheses to be tested are: (1) Human tumor blood flow increases by up to a factor of two at the onset of heating, but remains relatively constant thereafter during 60 minutes of heating at temperatures up to 44 degrees C, (2) human tumor blood flow decreases during a course of fractionated heating and (3) a correlation exists between tumor blood flow and tumor interstitial pH. Results thus far show that human tumor blood flow is not as sensitive to heat as that of most transplanted rodent tumors. The time-temperature response of blood flow will be studied at two intratumor points during each heat fraction by use of a thermal clearance technique. Extracellular pH will be measured at these same points prior to the first and fourth hyperthermia sessions. The results of this study will help provide a basic understanding of the physiology of human tumor blood flow and its response to hyperthermia.